Patient-operated orthopedic device

ABSTRACT

The invention serves patients having a fractured bone wherein separate parts of the bone have been immobilized by an external axial fixator, and the invention provides patient-operated mechanical structure to enable him to transiently distract spaced bone-anchored regions of the fixator. In one embodiment, the patient-operated mechanism is in the form of an accessory that is detachably mounted to the fixator; in another embodiment, the patient-operated mechanism is embodied in an external axial fixator, preferably of the so-called dynamic variety.

RELATED CASE

This application is a division of original application Ser. No.08/353,198, filed Dec. 9, 1994, now U.S. Pat. No. 5,788,695 and isdirected to subject matter non-elected in said original application.

BACKGROUND OF THE INVENTION

The invention relates to orthopedic devices in aid of bone-fracturerepair and, in particular, to a patient-operated device for stimulatedtransient distraction of fractured components of a bone.

External fixators of the nature disclosed in U.S. Pat. Nos. Re. 31,809and 4,621,627 rely upon an elongate central body of selectivelyadjustable length, with a bone-screw or bone-pin anchoring clamp at eachlongitudinal end of the body, with preferably a selectively lockedball-joint connection between each anchoring clamp and the body end towhich it is connected. Selectively available body length involvestelescoping body parts which are keyed against rotation and which can besecured to each other to hold a given setting of longitudinal spanbetween the anchoring clamps. Provision is made for periodic precisionincrements of length to be made in the clamped relation of thetelescoping body parts, by employing a length-adjusting jackingmechanism which may be an accessory device used by the surgeon toperiodically adjust overall fixator-body length, in the course of anumber of weeks of healing repair of the fracture; the accessory deviceis detachably applicable to the respective fixator-body parts, forincrementally jacking the fixator-body parts while momentarily releasingthe secured relation of these body parts, the secured condition of thebody parts being re-established before detaching the jacking mechanism.

In the course of normal leg fracture repair with such fixators, there isa period of several weeks during which the fixator-braced fracture issubjected to weight-bearing, i.e., the patient must stand and learn towalk with the clamped fixator. At the outset of this period, the fixator(via its bone-screw or bone-pin anchorages) takes almost all of thepatient's body weight, and in the ensuing course of time the fidelity ofbone-screw or bone-pin anchorage to the fractured bone graduallydegrades, thus causing the healing bone to assume an increasing fractionof transient weight-bearing loads, as when walking. The nature of suchtransient loads is one of transient compressional loading of thefracture, which has been identified as a therapeutic aid that enhancesthe strength and the speed of bone repair, with shortened duration ofthe period of the patient's need for his fixator.

Recognition of the therapeutic value of periodic transient compressionduring the weight-bearing phase of bone-fracture repair has given riseto various modifications of external-fixator construction, so as toprovide for more control of transient compressional loading. Suchdevices are sometimes called dynamic axial fixators, as in the case ofU.S. Pat. No. 5,320,622. Other forms of such devices are disclosed inSturtzkopf, et al. U.S. Pat. No. 5,026,372 and in Harris, et al. U.S.Pat. No. 4,502,473.

Applicant has discovered that therapy involving transient distraction ofa fracture is accompanied by callus development at the fracture site, toan extent which exceeds and which is superior to that resulting fromtransient compression associated with or in replication of theweight-bearing phenomenon discussed above. Moreover, therapy involvingtransient distraction has no relation or analogy to weight-bearing, andapplicant has found that transient distraction therapy does not requirethat the patient shall yet have progressed to the weight-bearing phaseof fracture repair.

BRIEF STATEMENT OF THE INVENTION

It is an object of the invention to provide an improved device andmethod for accelerated repair of a fractured bone.

Another object is to meet the above object with a device which can bepatient-operated without need for external power supply.

A specific object is to meet the above objects with an accessory devicewhich is applicable to existing commercially available external fixatorsand which is also applicable to a patient who is already fitted with andusing an external fixator.

Another specific object is to provide in an external fixator forpatient-operated periodic distraction of the fracture.

A general object is to meet the above objects with accessoryconstruction which is mechanically simple, readily patient-operated, andfunctionally reliable.

The invention in a preferred form achieves these objects by providingthe patient with a simple hand-operated mechanical device for removableapplication to the respective longitudinal ends of a dynamic externalaxial fixator, such that a patient's hand-cranked actuation will inducea transient distraction of the bone-anchored ends of the fixator, andtherefore transient distraction at the fracture site. In anotherembodiment, the patient-operated is distraction feature is a built-inpart of a dynamic external fixator.

DESCRIPTION OF THE DRAWINGS

Preferred and illustrative embodiments of the invention will bedescribed in detail, in conjunction with the accompanying drawings, inwhich:

FIG. 1, labelled "PRIOR ART", is a view in side elevation and partly inlongitudinal section, showing an external axial fixator with anaccessory jacking device for precise setting and adjustment of theeffective length of the fixator;

FIG. 2 is a similar view of a dynamic external axial fixator in explodedrelation with a patient-operated accessory device of the invention, fortransient distraction of the fixator;

FIG. 3 is a view in longitudinal section of the accessory device of FIG.2, to an enlarged scale;

FIG. 3A is a fragmentary view similar to FIG. 3, but showing amodification of the right end of FIG. 3;

FIG. 4 is a view generally similar to FIG. 3 for another embodiment, asan alternative for the accessory device of FIG. 2;

FIG. 5 is a simplified view in side elevation of a dynamic axial fixatorin which the transient distraction function of FIGS. 3, 3A or 4 is abuilt-in feature of the fixator per se;

FIG. 6A is an enlarged and exaggerated axial-end view of a cam in thestructure of FIG. 3, as viewed from the aspect 6A--6A of FIG. 3;

FIG. 6B is a graph to display a representative and presently preferredrelation of distraction as a function of cyclically repeated time;

FIG. 7 is an enlarged fragmentary longitudinal section to illustrate amodified cam and cam-follower construction; the section plane includesthe central longitudinal axis of the accessory device and is normal tothe transverse axis of cam rotation;

FIG. 7A is a view similar to FIG. 6A, for the modification of FIG. 7;

FIG. 8 is a view in side elevation, partly broken-away and inlongitudinal section, for another embodiment;

FIG. 9 is a longitudinal section of the embodiment of FIG. 8, taken at9--9 of FIG. 8;

FIG. 10A is a view in side elevation of a distraction-cam element ofFIGS. 8 and 9;

FIG. 10B is an end view of the element of FIG. 10A;

FIG. 11 is a fragmentary view of distraction-actuating components ofFIG. 8, for an actuated distraction condition;

FIG. 12 is a view similar to FIG. 11, for an actuated compressioncondition;

FIG. 13 is a simplified view of a first clamp structure applied to thedevice of FIGS. 8 and 9, to determine one phase of use, the sectionbeing taken at 13--13 in FIG. 8; and

FIG. 14 is a view similar to FIG. 13, to determine another phase of use.

DETAILED DESCRIPTION OF THE INVENTION

The prior art device of FIG. 1 is generally as shown and described insaid U.S. reissue patent, wherein an external axial fixator is seen tocomprise an elongate central body 10 of telescopically related inner andouter body parts which can be adjusted as to overall effective lengthvia a clamp bolt 11 which can secure these body parts to each other, fora given selected position of bolt 11 in an elongate slot 12 in the innerbody part. One end of one of the body parts, e.g., the outer body part13, has a ball-joint connection 14 to clamp means 15 for securelyclamped anchoring reference to one or more bone-screws or pins 16 thatwill be understood to have been driven into bone at offset in onedirection away from a fracture in the bone; the opposite end of theother body part, e.g., the inner body part, has a similar ball-jointconnection 17 to similar clamp means 15' for securely clamped anchoringreference to bone screws or pins 16' that have been driven into the boneat opposite offset from the fracture site. Both ball joints areselectively lockable, to retain a given angular relationship of the axisof body 10 to the respective axes of clamps 15, 15', as appropriate forparticular applications.

At its head or ball-joint connection end 18, the outer body part 13 hasa transverse bore that is adapted to receive and locate a first pin 19of a length-adjusting accessory 20; and similarly, at the opposite heador ball-joint connection end 21, the inner body part has a transversebore that is adapted to receive and locate a second pin 22 of theaccessory 20.

The length-adjusting accessory 20 comprises an internally threaded outertubular member 23 which mounts pin 19 at its projecting end, and aninner threaded rod has a wrenchable head 24 at the opposite end. Theinner threaded rod is wrench-actuated at 24 for adjustment of the extentof thread engagement within tubular member 21, and the head (24) end ofthe threaded rod seats on and is rotatable within a counterbore of aboss 25 which mounts pin 22. A lock nut 26, also engaged to the threadedrod, is run against boss 25 for locked retention of a given overallaccessory length, i.e., a given separation of the accessory-mounting ofpins 19, 22.

FIG. 2 shows an accessory device 28 of the invention, featuring amanually operable distraction function, in addition to thelength-adjustment function described for the prior art accessory deviceof FIG. 1. Specifically, insertion pins 30, 31 mount the accessory tothe body 32 of an external fixator which is preferably of the axiallydynamic variety, suitably as shown and described in said U.S. Pat. No.5,320,622. As shown, the lower pin 30 is mounted to a boss 33 which isaxially located at the head end 34 of an elongate rod or first body part35 that is in threaded engagement with the bore of an elongate tubularbody part 36; and the upper pin 31 is mounted to a sleeve 37 that isaxially slidable away from a fixed flange 38 on body part 36, foraccommodation of a manually actuated transient distracting displacementof pin 31 with respect to pin 30. The mechanism for patient-operation toachieve such distraction is contained within sleeve 37 and is manuallydriven by a partial rotary cranking actuation of a handle 49, as will bedescribed in greater detail in connection with FIG. 3.

Description of a dynamic axial fixator generally as shown in FIG. 2 isobtainable from said U.S. Pat. No. 5,320,622, which is herebyincorporated by reference. For present purposes, it suffices to notethat overall length of body 32 is established by a bolt 39 whichreleasably secures a first elongate body member 40 to an elongateintermediate body member 41 at a given relation of longitudinally guidedoverlap of members 40, 41. At its upper end, body member 40 has anenlarged head 42 which is transversely bored to provide for guidedinsertion of upper pin 31 of the accessory 28, and head 42 will beunderstood to be equipped with a ball-joint connection 17 to upper clampstructure 15' as described for the prior art in FIG. 1. A secondelongate body member 43 has an enlarged head 44 which is transverselybored to provide for guided insertion of the lower accessory pin 30, andhead 44 will be understood to be equipped with a ball-joint connection14 to lower clamp structure 15, as described for the prior art ofFIG. 1. A longitudinal guide rod 45 fixed to and projecting beyond theupper end of body member 43 has bidirectionally axial and resilientlysnubbed engagement to the laterally offset upper end 46 of intermediatebody member 41. Finally, a short link 47 is pinned on parallel pivotaxes in second body member 43 and in intermediate body member 41,wherein the two pivot axes define a geometric plane which issubstantially normal to the longitudinal axis of the fixator, namely,wherein the longitudinal axis is on the geometric alignment of ballcenters at the respective ball-joint connections 14, 17. Greater detailof the bidirectional snubbing action and structure will be found in saidU.S. Pat. No. 5,320,622.

In FIG. 3, parts which have already been identified will be recognized.In addition, the rotary but axially located relation of boss 33 to theinner body part 35 will be seen to be established by a collar 50 that ispinned at 51 to the unthreaded axially projecting shank end 52, adjacenthead 34. A low-friction washer 53, as of nylon, between collar 50 andboss 33 assures smoothly wrenched rotation of body part 35, to establishan initial span S between the respective fixator-engageable meansrepresented by pins 30, 31, for which condition sleeve 37 will beunderstood to be in its most leftward position, as in axially seatedengagement with flange 38, with span S as determined by the nominalinstalled overall length of the fixator body 32, the same having beenfixed by clamp bolt 39.

At its head end, the outer body part 36 is closed to establish anenlarged cylindrical land 54 for smooth axial guidance of sleeve 37, inits distraction displacement away from abutment with the shoulder orflange 38. As shown, this closed end comprises a first semicylindricalpart 55 that is an integral formation of body part 36, and a second andseparate semicylindrical part 56 that is bolted at 57 to secure parts55, 56 to each other and thus complete the continuity of land 54. Theconfronting adjacent surfaces of the semicylindrical parts 55, 56 aresimilarly concave to establish a flat cavity wall 58 as a surface ofcam-follower action, when handle 49 is operated to rotate a cam 59 inrising engagement with wall 58, thus incrementally and transientlyimparting a distraction displacement ΔS to the pin 31 with respect topin 30, i.e., to the fractured bone end secured at 15' with respect tothe other bone end secured at 15. A rotary cam 59, which may be acylindrical member or eccentric is mounted for gyrated rotation on afixed transverse axis 60, involving diametrically opposed cylindricalbearing formations 61, 61' that are journalled in diametrically opposedbearing bores in sleeve 37. These bearing formations 61, 61' also passthrough diametrically opposed short longitudinal slots 62, 62', by meansof which cam 59 is rotatable within the head end of the tubular part 36,and it is also keyed against rotation and incrementally axiallydisplaceable in slots 62, 62'. Various force-fitted engagements ofseparate parts in the succession 61, 62, 59, 62', 61' assure aneffectively shaft-mounted eccentric at 59, with provision for positivecam actuation via partial cranked rotation of handle 49.

FIG. 3A illustrates a construction alternative for the actuating end ofthe accessory 28 that has been described in connection with FIGS. 2 and3. In FIG. 3A, the distal end of threaded body part 35 is seen withinthe bore of outer tubular body part 36. Sleeve 37 mounts the pin 31 byway of an extended shank 31' of pin, extending across the full diameterof the sleeve, with threaded distal-end engagement to the sleeve, aslimited by a shoulder formation of pin 31. Within sleeve 37, the pinshank 31' freely passes through diametrically opposed openings intubular body part 36; these openings may be oval, with longitudinalorientation of their major-axis dimension so as to develop alongitudinal clearance 62 for accommodating the axially distractingdisplaceability of sleeve 37 (and its mounting pin 31) with respect tobody member 36. The cam 59' of FIG. 3A may be a cylindrical portion of aunitary part, which further comprises a distal-journal end 63 of smallerdiameter, a proximal-journal end 63' of greater diameter, a distalgrooved projection 64 for snap-ring retention, and a proximal-endprojection 64' for pinned mounting of the handle 49; it is noted (1)that the elements 64, 63, 63', 64' of this unitary part are all on theaxis of journal support by sleeve 37, with the axis of cam 59'eccentrically offset from axis 60, to the extent of desired distractingdisplaceability of pins 30, 31 with respect to each other, and that cam59' is rotatable (with suitable clearance, not shown) in a transversediametrically extending cam-following bore near the distal end of bodymember 36. In FIG. 3A, body member 36 is shown to have a solidly closeddistal end 36' in which the cam-following bore is formed. A springdetent pin 49' carried by handle 49 is detent-engageable at a localdetent recess in sleeve 37, to resiliently retain the longitudinallyoriented zero-distraction position of handle 49 when not in use.

In the embodiment thus far discussed, in connection with FIGS. 2 and 3,the longitudinal span S to accord with points of connection to aninstalled fixator is adjustably set (at 34), with sleeve 37 seatedagainst shoulder and with cam 59 at its low point in relation to thecam-follower wall 58. A partial rotation of the cam, manually impartedby handle 49, will engage cam 59 to wall 58 to effect a transientdistraction displacement ΔS, as sleeve 37 develops a correspondingincremental axial offset from shoulder 38. Having thus distracted thedynamic fixator, the handle 49 can allow the fixator to return to itsnormal axially fixated relation of the involved bone connections,astride the fracture. It is currently recommended that the patient betaught and instructed to perform such transient distraction cycles in arelatively rapid succession of as many as ten cycles, repeated onprescribed periodic intervals each day. Illustratively, the effectivecam rise may be 1 or as much as 2 mm, but preferably thedistraction-effecting cam rise is in the range 0.8 to 1.2 mm.

FIG. 6A is a simplified diagram to indicate present preference that,instead of cam 59 being cylindrical and eccentrically mounted withrespect to the rotary axis 60, cam 59 has a somewhat ovate profilewhereby to devote an extended proportion of its rise profile toachieving a substantially constant rate of rise, in the order of 4mm/second between the acceleration rise and deceleration rise needed tocomplete a given fully distracting displacement stroke of pins 30, 31with respect to each other. In FIG. 6A, this rise is a following of thechange of cam (59) profile from minimum radial extent R₁ to a maximumradial extent R₂, occurring as shown over a range of approximately 90degrees of cam rotation between points a and b of the cam profile. AndFIG. 6B is a graphical display of distraction displacement as a functionof time, showing the presently preferred order of uniform rate (3 to 5mm/sec) for substantially two-second dwells at each of the cam-followinglimits R₁, R₂, it being recommended that as many as ten recyclings ofthe indicated uniform-rate program be a typical protocol ofpatient-operated distraction.

It should also be noted that the described accessory of FIG. 3 lendsitself to a more elaborate protocol of use, particularly once thepatient has entered the weight-bearing phase of using his dynamicfixator. In this phase, the surgeon may prescribe incrementalcompressive action at the fracture site by reason of limited axialdisplaceability to transiently reduce the span S with eachweight-bearing step via the fractured but dynamically fixated bone. Topermit such transient compression, the inner body part 34 isincrementally wrenched so as to reduce the span S in incrementalprescribed relief of the sleeve/shoulder engagement; if handle 49 andcam 59 are in the low-point position as shown in FIG. 3, then any axialclearance of the cam 59 with respect to the cam-follower wall 58 will beopened while the corresponding axial clearance is opened between sleeve37 and shoulder 38. This shoulder clearance is available for theindicated transient incremental compressive action on the fracture site,with each weight-bearing step. And it will also be observed that, eventhough transient compressive action is available, the manually operateddistraction cycle is also available, as long as the rise of cam 59 issufficient to exceed the above-noted axial clearances.

In the embodiment of FIG. 3, transient distraction and/or compression ofthe fracture site involves transient axial displacement of sleeve 37with respect to shoulder 38. The embodiment of FIG. 4 provides analogousoperation by reason of transient axial displacement of an inner bodypart 65 with respect to an outer body part 66. The parts 65, 66 havelimited telescopically guided fit, the limitation being axial by reasonof a transverse pin 67 between diametrically spaced bores of the outer(tubular) body part 66, wherein pin 67 passes through a limited axialslot 68 of the inner body part 65. One (69) of the fixator-engageablepins 69, 70 of FIG. 4 is adjustably fixed to the inner body part 65, andthe other (70) is adjustably fixed to the outer body part 66. To thisend, the mounting hub 71 on pin 69 is shown to be carried at the exposedouter threaded end of body part 65, with nuts 72, 73 for fine setting ofa given clamped axial position of pin 69; and the mounting hub 74 of theother pin 70 is shown to be selectively clamped at any given one ofplural equally spaced locating grooves 75 (a,b,c) in the outer surfaceof body part 66, clamping being via three equally spaced set screws 76,only two of which appear in FIG. 4. A handle 49' and rotary cam 59',eccentrically offset from a transverse axis 60' of rotation in a fixedhead 77 of body part 66, perform analogously to the action described forFIG. 3, except that in FIG. 4, manually cranked rotation of cam 59'through its rise will result cam driven incremental distractingdisplacement of the adjacent cam-following rod end of inner body part65, to the extent shown at ΔS' in FIG. 4. For set-up purposes, it willbe noted that the fixed spacing of intervals between grooves 75a, 75b,75c enables rough increments to accommodate a given fixator requirementfor the pin-to-pin span S', and that the threaded extent of the exposedend of inner body part 65 need be only slightly in excess of the spanbetween two adjacent outer body grooves. Operation and fixatoradaptation of the accessory of FIG. 4 are essentially as described forFIG. 3, except that optional basic span settings are greater for thecase of FIG. 4, for example to the span (S'+A) or to the span (S'+A+B),beyond the span S' shown, all in accordance with whether hub 74 is setat groove 75b or at groove 75a.

In FIG. 5, the manually operated function of transient distraction is abuilt-in feature of a dynamic axial fixator 80 of the general natureshown for the fixator in FIG. 2, but without requiring an accessory (28)to perform the transient distraction. In FIG. 5, the head end 44' of theouter body part 43' is slightly more axially elongate than is shown forhead 44 of FIG. 2. And an idler arm 81 will be understood to be pivotedat 82 to body part 43' on an alignment parallel to and axially offsetfrom the lower pivot for link 47. Idler arm 81 will also be understoodto be accommodated within a recess in head 44'. For the unstressedcondition shown for fixator 80 in FIG. 5, link 47 is oriented transverseto the longitudinal axis of the fixator body, and a projection 83 on theadjacent confronting end of intermediate body part 41' is poised forengagement by arm 81, with arm 81 substantially parallel to link 47. Fortransient distraction, a rotary cam or eccentric 84 is shown mounted forrotation on a transverse axis, schematically indicated at 85, in head44'. It will be understood that the cam or eccentric 84 can beshaft-driven on axis 85, by a manual crank, not shown in FIG. 5 but asshown in FIG. 3 or FIG. 4. Eccentric throw incrementally distractsbone-screw clamp 15' with respect to bone-screw clamp 15.

In the modification of FIG. 7, the annular body member or sleeve 37again overlaps and is guided for limited axial displacement on thetubular body member 36; and the fixator-engageable rod 31 derives fixedmounting from sleeve 37, at diametrically opposed locations. Rod 31passes through tubular body member 36 via diametrically opposed slots62, of sufficient axial extent to provide anti-rotational guidance ofbody member 36 with respect to sleeve 37 for all cam-driven axialdisplacements.

An important. feature of FIG. 7 is the characterizing of cam andcam-follower action, which is further illustrated in connection withFIG. 7A. FIG. 7A displays only the cam 80, which is integral with orotherwise fixedly related to a proximal land 81 of greatest diameter andto a distal land 82 of lesser diameter; the land 81 will be understoodto derive journal support in a diametrically oriented bore 83 (FIG. 7)through one side of sleeve 37, and land 82 will be understood to derivefurther journal support in a counterbore (not shown) through theopposite side of sleeve the operative profile of cam 80 interposedbetween lands 81, 82.

Cam 80 is characterized by a flat surface 84 which is normal to acentral plane of symmetry through the axis of cam rotation, determinedby the aligned centers of lands 81, 82. Outer rounded lobes 85, 85'symmetrically terminate the respective ends of surface 84 and determinean overall cam width W, approximately 75 percent of which isattributable to surface 84. The contour of cam 80 is completed bysloping back sides which are respectively tangent to the profiles oflobes 85, 85' and of land 82.

The described features of cam 80 will be recognized in FIG. 7, in thecontext of coacting cam-follower structure of the tubular member 36;wherein the drawing illustrates the relation of parts for an instantduring the course of a distracting actuation of cam 80, namely, with cam80 rotated a small fraction α₁ of its full range α₂ of displaceabilityfrom a zero-distraction condition wherein the flat surface 84 is normalto the central axis 86 of the tubular body member 36. Cam-followerstructure is provided by diametrically opposite matching edges 87 ofdiametrically opposite generally rectangular openings, of body axiallength L and transverse width W₂ ; the edges 87 may be said to lie in ageometrical plane that is normal to the central axis 86. Since bodymember 36 is tubular, the back wall of these rectangular openings isclosed and defined by a plate 88, seated against a shoulder and fixed inposition by a transverse pin 89. The transverse width dimension W₂slightly exceeds the width W₁ of cam 80, but the length dimension Lpreferably is less than the width W₁ of cam 80.

In the course of continuing cam-80 rotation in the clockwise direction,the lower lobe 85 rides on both of the edges 87 of the opposedrectangular openings of tubular member 36, thus drawing sleeve 37 andits rod 31 in further distraction of the space S between the two rods30, 31. And since the length L is preferably less than the cam width W₁,there comes a point at which cam lobe 85' strikes the back-closure plate88. For the form shown, this limiting point determines the maximum angleα₂ of hand-crank (49) operation of cam 80, namely approximately 45degrees away from the zero-distraction position, at which point a iszero and hand crank 49 is parallel to the body axis of tubular member36.

Thus far, all distraction displacements have been referred to astransient, meaning a hand-cranking of the full rise of the rotary cam ora part of said rise, as may be prescribed by the surgeon, the same beingfollowed by return to the position of zero distraction. But it has alsobeen indicated that a plurality of sequential distractions may beprescribed for a given event in a patient's therapy, in which case acrank extension on the handle, as at 86 in FIG. 4, may facilitate thepatient's easy development of the sequence of distractions, throughcontinuous manually driven rotation via crank extension 86.

While the invention has been described in the foregoing with particularreference to specific embodiments, it is to be appreciated that theinvention is not limited to the embodiments described, but isencompassed by the broad wording of the appended claims which envisagemodifications and variations to the described embodiments which wouldoccur to those possessed of the relevant skills and knowledge. Inparticular, while the invention has been described in the foregoing withparticular reference to orthopedic distraction devices, it would be asimple matter to modify the described devices to be capable of providingcompressive displacement, either instead of or, selectively, in additionto distractive displacement. For example, the cam structure shown inFIG. 6A could be inverted about a horizontal plane bisecting the rotaryaxis 61 so as to provide compression rather than distraction, and othermodifications which will readily occur to those possessed of therelevant skills could be made for enabling selective distraction and/orcompression. Also, for example, if in FIG. 7 the described journalsupport of cam 80 in sleeve 37 were 180-degrees reversed, with the camsurface 84 flat against back plate 88 for a location of zerocompression, any rotation of cam 80 would entail compressivedisplacement of the rods 30, 31 by reason of cam lobe coaction withplate 86.

Still further, recent clinical studies have indicated a desirable aspectof patient-actuated distraction whereby a lost motion designed into theactuator enables the patient to crank the actuating handle approximately45° away from its normally stowed position of parallel orientation withrespect to the elongation axis of the fixator body, before any cammed orother distracting displacement becomes operative. The embodiment ofFIGS. 8 and 9 is illustrative of such a device, which will be understoodto be built into the head end of a tubular outer body member 136; member136 has adjustably threaded engagement to the elongate stem of an innerbody member 135 which carries one of the fixator-engageable pins (notshown in FIGS. 8 or 9, but analogous to the showing at 30 in FIG. 3). Atthe head end of body member 136, an outer sleeve 137 mounts the otherfixator-engageable pin 131 at diametrically opposite locations, with pin131 passing through axially short slotted openings 162 which establishsufficient longitudinal clearance to accommodate axially distractingdisplaceability of sleeve 137. Within a counterbore at the head end ofbody member 136, a cam-follower element 155 in the form of acylindrical. plug is secured by pin means 156 to body member 136, andplug 155 features a transverse bore of generally square section; axiallyspaced walls 170, 171 of this generally square section providecam-follower surfaces, for hand-actuated rotary displacement of asingle-piece cam component 172, shown in the form of a crank shaft, ingreater detail in FIGS. 10A and 10B.

The cam component 172 is seen to comprise spaced cylindrical bearings173, 174 which will be understood to derive journal support indiametrically opposite large and small bores in sleeve 137. A crank pinelement 175 integrally connects the spaced bearings 173, 174; and a studformation 177 outward of bearing 173 provides a rugged means ofhandcrank 149 connection, the same being shown pinned at 178, to retainthe connection. The stud formation 176 is suitably of square section,engaging a bore of similar square section in handle 149, and a lockingpin 177 secures the square stud-to-bore engagement, with Allen-headdriven thread engagement in the handle. A detent 149' carried by handle149 provides releasable engagement to a central detent notch in theadjacent end of pin 131, to releasably hold the retracted position ofhandle 149, parallel to the longitudinal axis of body member 136.

The generally square section of the transverse bore of cam-follower plug155 is sized to meet two criteria: first, angular throw of crank pin 175extends free of cam-actuating engagement with either of the axiallyspaced cam-follower wails 170, 171 of the square-section, over a rangeof approximately ±45 degrees of rotary lost motion, and second, theentire crankshaft element 172 is configured at reduced lower-bearing end174 to permit simple threading assembly of crank pin 175 and bearing 174regions via the sleeve bore in which the larger bearing 173 isjournalled, and via the transverse square section bore in plug 155. Thisassembly is retained by snap-ring engagement to a peripheral groove 178in the small-bearing end of crankshaft element 172.

The above-noted recent clinical studies have indicated afurther-desirable aspect of patient-actuated distraction, whereby thedescribed patient-operated distraction phase is limited to a period ofsay four or five weeks as from the end of the first week (of initiallyrigid bone fixation) to the end of the fifth week, the same to befollowed throughout a remaining period of fixation wherein the describeddevice of FIGS. 8 and 9 is resettable to a fixed compression of thefracture site; in this period of fixed compression, the same camstructure is relied upon to achieve a fixed compression displacement ofthe same magnitude as the patient-operated distraction displacement, butof course in the opposite direction. To assure that the patient can onlyoperate the device for transient distraction as prescribed, provision ismade in the form of a limit stop for preventing handle (149) operationin the wrong direction; provision is also made to assure that handle(149) cannot be patient-operated during his fixed-compression phase offracture repair.

FIG. 13 is a simplified sectional view at a part of handle 149 to show ahinged circumferential clamp 180 secured by a clamp bolt 181 so as toposition a stop projection 183 alongside the finger-engageable end ofhandle 149, thus limiting rotary actuation of handle to a single side ofthe at-rest position of parallel relation to the axis of body 136,namely, limitation to the side on which manually actuated distraction ispossible, to the fully distracted relation depicted in FIG. 11.

On the other hand, when the physician determines that the period ofpatient-operated distraction has been completed and that fixedcompression should be applied, the physician has two simple changes tomake in the device of FIGS. 8 and 9. First, of course, he should removethe clamp 180 of FIG. 13, but before applying a similar clamp 184 tobody 136 (FIG. 14), the locking pin 177 should be removed to permithandle 149 to assume a 90°-displaced engagement to the square studformation 176 of cam 172. In this condition, handle 149 will extendnormal to the axis of body 136 when the internal parts have the neutralrelation depicted in FIG. 9. Having made this new square-stud tosquare-bore engagement, the locking pin 177 can be reset through asecond bore 177' (see FIG. 10A) in stud 176, to lock the engagement, andthe handle then actuated the 90-degrees of rotation necessary forrealignment parallel with the axis of body 136. In the course of makingthis 90 degree displacement, and following an initial lost-motion handledisplacement of about 45 degrees, the crankpin 175 of cam 172 willengage cam-follower surface 171, to accomplish the compressiondisplacement, thus placing internal parts in the relation depicted inFIG. 11. Once the full-compression position (of handle 149) has beenachieved, clamp 184 is set to body 136 (see FIG. 14), with its twoprojecting stops 185, 186 fixed to opposite sides of thefinger-engageable end of the handle.

In a recommended use of the device of FIGS. 8 and 9, as in conjunctionwith a fixator of the variety of FIG. 1 or of FIG. 2, a recommendedprogram of use is for the first week to be one of axial fixation, i.e.,no compression and no distraction. Then for the next 4 to 5 weeks, thepatient should be instructed to use the distraction feature as a rapidsequence of distraction-displacement cycles, e.g., a. sequence of tencycles each day, wherein the operative throw is of cam 172 is in therange 1 to 2 mm (+ΔS). Upon the physician satisfying himself that theprogress of fracture healing has sufficiently advanced, the describedresetting to a fixed compression (-ΔS) is made for the remaining use ofthe fixation, with an option, in the case of the dynamic fixator of FIG.2, to permit a period of dynamic compression via the fixator itselfwhile the patient is in the weight-bearing phase of recovery.

What has been said for the device of FIGS. 8 and 9 will be understood tobe equally applicable for the case of a fixator attachment, (asdescribed for use with the fixator of FIG. 2), as well as for the caseof embodiment in the construction of an external fixator per se. And inthe case a lost-motion displacement prior to cam/cam-followerengagement, there is a psychological advantage in providing theindicated approximately 45 degrees of lost motion because this enablesthe patient to get a better grip on the handle for the relatively rapidsuccession of cranking cycles he must make in the next 45-degree range,to achieve the described cyclical recurrence of distraction (+ΔS).

What is claimed is:
 1. The method of operating a distraction device forselective periodic distraction of a fractured bone that has been set forretention by an external fixator having an elongate distensible bodyconnected at its longitudinal ends via bone screws or bone pins to boneon opposite sides of the fracture, wherein the distraction is via ahand-crank operated transient distention of said body, wherein a maximumdistraction displacement is in a range up to 2 mm, and wherein the rateof distracting displacement is in the range 3 to 5 mm per second over asubstantial fraction of the displacement to maximum.
 2. The method ofclaim 1, in which said rate is substantially 4 mm per second.
 3. Themethod of claim 1, wherein a cycle of use includes a hold of at leastone second at maximum distraction before reducing the distraction. 4.The method of claim 3, wherein the rate of reducing distraction isapproximately the same as that of increasing distraction.
 5. The methodof claim 4, in which a dwell of at least one second is provided afterfull reduction of distraction and prior to commencement of anext-succeeding cycle of distraction.
 6. The method of claim 5, in whichcycles repeat at intervals of 5 to 10 seconds.
 7. The method of claim 3,in which each therapeutic use of the method involves a succession of atleast 5 cycles, each cycle being of 5 to 10 second periodicity.
 8. Themethod of claim 1, in which the rate of reducing distraction isapproximately the same as the rate of increasing distraction.
 9. Themethod of using a patient-operated distraction device to selectivelyapply a distracting displacement to a bone fracture which has been setby an external fixator having an elongate distensible body connected tobone-screw or bone-pin clamps at the respective ends of said fixatorbody, with bone-screws or bone-pins anchored in bone at spaced locationson opposite offsets from the fracture, wherein the distraction devicecomprises:(a) an elongate internally threaded tubular body part and anelongate externally threaded body part engaged to said tubular bodypart, with a longitudinal end of said tubular body part extending at oneend of said device and with the opposite longitudinal end of saidthreaded body part extending at the other longitudinal end of saiddevice; (b) first fixator-engageable means in axially retainedengagement with and supporting said threaded body part at said oppositelongitudinal end for selective rotation with respect to said firstfixator-engageable means; (c) second fixator-engageable means in axiallydisplaceable anti-rotational relation with said tubular part at said onelongitudinal end; and (d) manually operated cam means longitudinallyinterconnecting said second fixator-engageable means and said tubularbody part; said cam means being characterized by a profile such thatmanual actuation can produce a maximum distracting displacement in therange up to 2 mm; said method comprising the steps of:(i) adjusting thelength of the device to accommodate the space between said clamps; (ii)engaging the first and second fixator-engageable means to the respectiveends of the fixator body; (iii) manually operating said cam means todrive said fixator-body ends and therefore said clamps in a cycle oftransient distracting displacement of said clamps, followed by acorresponding but contracting displacement of said clamps; and (iv)repeating said cycle for a predetermined number of successive cycles.10. The method of claim 9, wherein the predetermined number ofsuccessive cycles is at least five.